Referring to FIGS. 1A-1D, light shading film 12 such as chrome is provided in a desired pattern on mask substrate 11 of quartz glass, and phase shift layer 14 for increasing the intensity of projected light is selectively applied using a transparent material of which refractive index n is larger than 1.
As illustrated in FIG. 1A, light passes through either phase shift layer 14 of which mask refractive index meets the condition of n&gt;1 (1), or through an area of which the refractive index meets the condition of n=1 (2). The transmitted light energy according to the intrinsic light absorption coefficients of each area through which light passes is illustrated in FIG. 1B. Here, the thickness of the phase shift layer is adjusted to make the phase shift between the two areas 180.degree..
FIG. 1C illustrates the intensity of light according to the transmitted light energy, in which the intensity of light passed through phase shift layer 14 is weaker as much as .DELTA.i due to the differences in light transmissivities.
FIG. 1D illustrates a state of photoresist 13 after development, in which the profiles appear to be different due to the differences in intensities of areas (1) and (2).
Hereinafter, a conventional phase shift mask manufacturing method will be described with reference to FIGS. 2A to 2J.
Light shading film 12 is formed on quartz glass substrate 11 (FIG. 2A). Photoresist 13 is applied to quartz glass substrate 11 (FIG. 2B). Photoresist 13 is exposed to light by an E-beam using direct lighting equipment, and a plurality of patterns of photoresist 13 of a uniform interval are developed and dried as illustrated (FIG. 2C). Light shading film 112 is etched using patterned photoresist 13 as a mask (FIG. 2D). The remainder of photoresist 13 on light shading film 12 is removed (FIG. 2E). Phase shift layer 14 is applied on quartz glass substrate 11 and the patterns of light shading film 12 (FIG. 2F). E-beam photoresist 13' is applied on phase shift layer 14 (FIG. 2G). Photoresist 13' is developed and dried to remain on pairs of light shading films 12 (FIG. 2H). Phase shift layer 14 is etched using the patterns of photoresist 13' as a mask (FIG. 2I), and the patterns of photoresist 13' are removed (FIG. 2J).
With a phase shift mask manufactured using such a conventional method, inequalities in a transmitted image may occur due to the difference of the light transmissivity coefficients between an air area of which refractive index is 1 and phase shift layer 14 of which refractive index is larger than 1. Since the result of such a conventional method appears as a form of resist profile as illustrated in FIG. 1D, a problem may result from the process, and efforts to adjust the inequality by excessively exposing in order to compensate for an insufficiently developed area can lead to a change from the desired pattern.